Floorboards for floorings

ABSTRACT

Floorboards for making a floating floor have a core ( 30 ) which comprises at least two layers of material (L 1 , L 2 ), which are arranged at different distances from the surface layer ( 31 ), and which differ in respect of material properties or material composition. Semi manufactures for making such floorboards are also disclosed.

TECHNICAL FIELD

The invention generally relates to the field of core materials forfloorboards. The invention relates to floorboards provided with suchcore materials, and floor elements of such core materials intended formaking floorboards. The invention is particularly suited for use infloating floors such as laminate flooring as well as floorboards with asurface layer of veneer or wood, but is also usable in other similarfloorings.

More specifically, the invention relates above all to floors of the typehaving a core and a decorative surface layer on the upper side of thecore.

FIELD OF APPLICATION OF THE INVENTION

The present invention is particularly suitable for use in floatingfloors, which are formed of floorboards which are made up of surfacelayers of decorative laminate, veneer or decorative plastic material, anintermediate core of wood-fiber-based material and preferably a lowerbalancing layer on the rear side of the core. The following descriptionof prior-art technique, problems of known systems and objects andfeatures of the invention will therefore, as a non-restrictive example,be aimed above all at this field of application and in particularlaminate flooring and wood flooring with a core of wood slates formed asrectangular floorboards intended to be mechanically joined on both longsides and short sides. However, it should be emphasized that theinvention can be used in optional floorboards having a core and adecorative layer arranged on the core.

BACKGROUND OF THE INVENTION

Laminate flooring usually consists of a core of a 7-8 mm fiberboard, a0.2-0.8 mm thick upper decorative surface layer of laminate and a0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper orlike material. The surface layer provides appearance and durability tothe floorboards. The core provides stability and helps, together withthe surface layer, to give the floorboard sufficient impact strength.The balancing layer keeps the board plane when the relative humidity(RH) varies during the year. The floorboards are laid floating, i.e.without gluing, on the subfloor. Traditional hard floorboards infloating flooring of this type are usually joined by means of gluedtongue-and-groove joints (i.e. joints involving a tongue on onefloorboard and a tongue groove on an adjoining floorboard) on long sideand short side.

In addition to such traditional floors, which are joined by means ofglued tongue-and-groove joints, floor-boards have recently beendeveloped which do not require the use of glue and instead are joinedmechanically by means of so-called mechanical locking systems. Thesesystems comprise locking means which lock the boards horizontally andvertically. The mechanical locking systems are usually formed bymachining of the core of the board. Alternatively, parts of the lockingsystem can be formed of a separate material, such as aluminum, which isintegrated with the floorboard, i.e. joined with the floorboard inconnection with the manufacture thereof.

The main advantages of floating floors with mechanical locking systemsare that they can easily and quickly by laid by various combinations ofinward angling and snapping-in. They can also easily be taken up againand used once more at a different location. A further advantage of themechanical locking systems is that the edge portions of the floorboardscan be made of materials which need not have good gluing properties.

Laminate flooring and also many other floorings with a surface layer ofplastic, wood, veneer, cork and the like are made by the surface layerand the balancing layer being applied to a core material.

The first generation laminate flooring, so-called HPL flooring, was madeby providing a 6 mm thick particle board with a 0.8 mm surface layer ofdecorative high pressure laminate, usually referred to as HPL. HPL ismade in a separate operation where a plurality of impregnated sheets ofpaper are compressed under high pressure and at a high temperature to alaminate board.

Later the second generation laminate flooring was developed, which isbased on a more modern principle where both manufacture of thedecorative laminate layer and the fastening to the fiberboard take placein one and the same manufacturing step. Impregnated sheets of paper areapplied directly to the board and pressed together under pressure andheat without any gluing. As a rule, the surface layer is about 0.2 mmthick. This direct laminated flooring, usually referred to as DLflooring, whose main advantage is that the production cost is lower, wasfirst inferior to HPL flooring owing to, inter alia, a lower degree ofimpact strength and lower moisture resistance. The quality properties ofthe DL flooring, however, were significantly improved when the particleboard was replaced by a qualified HDF type fiberboard—high densityfiberboard. The HDF board was considerably harder than the particleboard and more resistant to moisture. Thus, the impact strength andmoisture resistance of the DL flooring could be improved. As this HDFboard was also being manufactured in increasingly larger volumes, thecost was reduced and DL flooring with an HDF core became number one onthe market. Although the particle board is considerably cheaper thanHDF, the DL technology combined with HDF is altogether less expensive.DL flooring now had quality properties equivalent to those of HPLflooring but was at the same time essentially less expensive.

At this time when DL flooring was being sold in larger quantities thanHPL flooring, the laminate flooring was joined using a traditionallocking system consisting of tongue, groove and glue. HPL flooring witha core of particle board was easier to glue than DL flooring with a coreof HDF. When the mechanical joint systems were developed, also thisproblem was eliminated, and in a short time DL flooring with a core ofHDF captured 90% of the market.

In addition to the above two methods, a number of other methods are usedto manufacture floating floors and provide different core materials witha surface layer. A decorative pattern can be printed on the surface ofthe core, which is then, for example, coated with a wear layer. The corecan also be provided with a surface layer of wood, veneer, decorativepaper or plastic sheeting, and these materials can then be coated with awear layer.

As a rule, the above methods result in a floor element in the form of alarge board which is then sawn into, for instance, some ten floorpanels, which are then machined to floorboards.

In all cases, the above floor panels are individually machined alongtheir edges to floorboards. The machining of the edges is carried out inadvanced milling machines where the floor panel is exactly positionedbetween one or more chains and bands mounted, so that the floor panelcan be moved at high speed and with great accuracy past a number ofmilling motors, which are provided with diamond cutting tools or metalcutting tools, which machine the edge of the floor panel. By usingseveral milling motors operating at different angles, advanced jointgeometries can be formed at speeds exceeding 100 m/min and with anaccuracy of ±0.02 mm.

JP-20011329681 discloses a floorboard having a multilayer core and asurface layer comprising wood veneer and a vapor proof layer arrangedbetween the veneer and the core. The core comprises a middle layer ofplywood and upper and lower layers of MDF.

Definition of Some Terms

In the following text, the visible surface of the installed floorboardis called “front side”, while the opposite side of the floorboard,facing the subfloor, is called “rear side”. The sheet-shaped startingmaterial that is used is called “core”. When the core is coated with asurface layer closest to the front side and preferably also a balancinglayer closest to the rear side, it forms a semimanufacture which iscalled “floor panel” or “floor element” in the case where thesemimanufacture, in a subsequent operation, is divided into a pluralityof floor panels mentioned above. When the floor panels are machinedalong their edges so as to obtain their final shape with the jointsystem, they are called “floor-boards”. By “surface layer” are meant alllayers applied to the core closest to the front side and coveringpreferably the entire front side of the floorboard. By “decorativesurface layer” is meant a layer which is mainly intended to give thefloor its decorative appearance. “Wear layer” relates to a layer whichis mainly adapted to improve the durability of the front side. Inlaminate flooring, this layer as a rule consists of a transparent sheetof paper with aluminum oxide added, which is impregnated with melamineresin. By “reinforcement layer” is meant a layer which is mainlyintended to improve the capability of the surface layer of resistingimpact and pressure and, in some cases, compensating for theirregularities of the core so that these will not be visible at thesurface. In high pressure laminates, this reinforcement layer usuallyconsists of brown kraft paper which is impregnated with phenol resin.

By laminate flooring is meant a floor board with a surface layer of athermosetting laminate comprising one or more paper sheets impregnatedwith a thermosetting resin.

A core consisting of wood slates which are glued to a surface andbalancing layer of wood is called “lamella core”. The slates have afiber orientation which is perpendicular to the fiber orientation of thesurface and balancing layers

The outer parts of the floorboard at the edge of the floorboard betweenthe front side and the rear side are called “joint edge”. As a rule, thejoint edge has several “joint surfaces” which can be vertical,horizontal, angled, rounded, beveled etc. These joint surfaces exist ondifferent materials, for instance laminate, fiberboard, wood, plastic,metal (especially aluminum) or sealing material. By “joint edge portion”are meant the joint edge of the floorboard and part of the floorboardportions closest to the joint edge.

By “joint” or “joint system” are meant coacting connecting means whichconnect the floorboards vertically and/or horizontally. By “mechanicallocking system” is meant that the joining can take place without gluehorizontally parallel to the surface and vertically perpendicular to thesurface. Mechanical locking systems can in many cases also be joined bymeans of glue which could be applied in the joint or between the rearside and the subfloor. By “floating floor” is meant a floor withfloorboards which are only joined along their respective joint edges andthus not glued to the subfloor. In connection with movement due tomoisture, the joint remains sealed. Movement due to moisture takes placein the outer areas of the floor along the walls concealed under the baseboards. By “HDF” are meant board materials that are referred—to on themarket as-high-density-fiberboard. HDF consists of ground woodfibers-joined by means of a binder. By particle board is meant a boardmaterial comprising wood particles joined by means of a binder.

The above techniques can be used to manufacture laminate floorings whichare highly natural copies of wooden flooring, stones, tiles and the likeand which are very easy to install using mechanical joint systems. Thelength and width of the floorboards are as a rule 1.2 * 0.2 m and thethickness is as a rule 7-8 mm.

Recently also laminate flooring with other formats and other thicknesseshave been introduced on the market. Formats having a length of 1.2 m, awidth of 0.4 m and a thickness of about 11 mm are used, for instance, toimitate stones and tiles. Laminate floor may also be produced in lengthsof 1.8-2.4 m and widths of 0.2 m. All such floorboards will be heavy anddifficult to handle in connection with transport and installation sinceHDF has a density of about 900 kg/m³. Besides the cost of material foran 11 mm HDF core is high. There is thus a great need to lower the costand also the weight of the core in a thick or large laminate flooringboard, but also in laminate flooring of normal thickness. The sameapplies to similar flooring having other surface layers such as veneer,plastic etc. For parquet flooring with a surface layer of 2-3 mmhardwood and a lamella core, the cost of the surface layers isconsiderable. The market for floating floors could increasesignificantly if the cost of the floorboard could be lowered and if theweight could be reduced.

Laminate flooring has a hard surface layer which produces a high soundlevel in the room as people walk on the floor, wearing shoes. This is adisadvantage that reduces the possibility of using the floor especiallyin public surroundings.

Prior-Art Technique and Problems Thereof

To facilitate the understanding and description of the present inventionas well as the knowledge of the problems behind the invention nowfollows with reference to FIGS. 1-3 in the accompanying drawings.

FIGS. 2 a-2 c show manufacture of an HPL flooring. A wear layer 34 of atransparent material with great wearing strength is impregnated withmelamine with aluminum oxide added. A decorative layer 35 of paperimpregnated with melamine is placed under this layer 34. One or morereinforcing layers 36 a, 36 b of core paper impregnated with phenol areplaced under the decorative layer 35 and the entire packet is placed ina press where it cures under pressure and heat to an about 0.5-0.8 mmthick surface layer 31 of high pressure laminate (HPL). FIG. 2 c showshow this surface layer 31 can then be glued together with a balancinglayer 32 to a core 30 to constitute a floor element 3. Due to theseparate gluing operation, HPL flooring may be produced with a varietyof different core materials such as HDF, particle boards and plasticmaterial sheets. All HPL floors are however produced with a core of onematerial only.

FIGS. 2 d and 2 e illustrate manufacture of a DL flooring. A wear layer34 in the form of an overlay and a decorative layer 35 of decorationpaper is placed directly on a core 30. All three parts and, as a rule,also a rear balancing layer 32 are then placed in the press where theycure under heat and pressure to a floor element 3 with a decorativesurface layer 31 having a thickness of about 0.2 mm. Direct laminate hasusually no reinforcing layer. The capability of the laminate edge toresist impact and moisture is quite dependent on the properties of thecore material. Therefore use is made of a high quality material withhigh density and moisture resistance such as HDF. The cost of materialfor HDF is significantly higher than that for particle board. Theproduction method of direct lamination is a factor that limits thepossibilities to use various core materials since the decorative layeris fixed to the core by the melamine resins in the decorative paper. Theresin penetrates into the wood fibers of an HDF material and binds thesurface layer to the core. The majority of all DL floors are producedwith a HDF core. Some low quality floors are produced with a core of MDFor particle board. All DL floors however are based on a core made of asingle material.

FIG. 3 a shows an example of a traditional laminate or veneer flooringwith a surface layer 31 of, for instance, direct laminate (DL) or 0.6 mmveneer, a core 30 of HDF and a balancing layer 32 of laminate or veneerthat are joined by tongue, glue and joint. FIG. 3 b shows an example ofa laminate flooring with a surface 31 of HPL, a core of HDF and amechanical locking system which consists of a strip 6 and a lockingelement 8 of aluminum and which coacts with a locking groove 14 formedin the core 30. In order to fix the strip to the core and to reachsufficient locking strength, the core is generally made of HDF.

FIG. 3 c shows an example of a laminate flooring with a surface 31 ofDL, a core 30 of HDF and a mechanical locking system 6, 8, 14 which hasbeen formed from the core 30 of the floorboard. A core of HDF is in thiscase necessary for the locking system to obtain the required strengthand function. The surface layer 31 could be wood or HPL. A wood surfacecould be combined with a core of HDF or plywood consisting of differentwood layers which may be made of different wood materials.

FIG. 3 d shows an example of a laminate flooring with a surface 31 ofDL, a score of HDF and a mechanical joint system with a locking element8 and a locking groove 14 in the upper part of the tongue groove.

FIG. 3 e shows a parquet flooring, seen from the long side, with athickness of about 15 mm, which has a surface layer 31 of e.g. 3 mm oak.The core consists in this example of different kinds of wood. A harderkind of wood 30 a, 30 b is to be found at the joint edge portionsforming the mechanical locking system 7, 7′. Between these joint edgeportions, the core 30 consists of wood slats 30 c made of a soft andinexpensive kind of wood. The slats 30 c are joined with the surfacelayer 31 and the balancing layer 32 by gluing. They often contain knots,cracks and the like. The surface layer 31 of wood must have a sufficientthickness to bridge these irregularities as well as the joints 37between the slats 30 c of the core. Such a lamella core is generallyless expensive than an HDF core and gives a more stable floor board.

These floorboards suffer from a number of problems which are above allrelated to cost and function.

The HDF core that is required to give a laminate flooring or veneerflooring sufficient impact resistance in the surface and at the jointedges has substantially the same high quality in the entire floorboard.The density of a HDF core might vary between the parts closest to thesurface and some other parts in the centre of the core but all partscontain the same type of wood fibers and binders. This overall highquality is not necessary, for instance, in the inner and rear parts ofthe floorboard.

Penetration of moisture into a floorboard takes place above all in theupper portions of the joint edge closest to the surface and it is inthese portions that the HDF material is necessary. In the other portionsof the floorboard lower quality properties would be sufficient.

To be able to form a mechanical locking system with projecting parts,the joint edge and thus also the core of the floorboard must as a rulebe of good quality. Also in this context, the high quality is onlynecessary in certain parts of the joint edges.

A parquet flooring with a lamella core has a wear layer of about 3 mm.This is needed above all to give the surface sufficient impact strengthand to bridge the spaces between the wood slats of the core so as toprevent them from telegraphing through the surface layer and becomingvisible in the surface. The surface layer is currently protected by astrong varnish and regrinding takes place only rarely or not at all.Consequently, the thickness of the wear layer could be reduced if theremaining problems could be solved.

The above problems result in a high cost of material and a high weight.The hard surface produces an undesirable sound level.

To counteract these problems, different methods have been employed. Themain method is to reduce quality and density of the HDF board. DLflooring is also made with a particle board as core material. Thesemethods result in a lower cost and a lower weight, but at the same timethe impact strength is insufficient, the boards are sensitive tomoisture and the mechanical joint systems have low strength and a poorfunction.

Parquet flooring is made with a core of particle board, HDF or plywood.As a rule, these materials are more expensive than a core of slats. Acore of slats also reduces the board's movement due to moisture betterthan other board materials since the slats of the core are placedperpendicular to the longitudinal direction of the board. This meansthat the fiber direction of the slats is perpendicular to the fiberdirection of the surface layer. Such a fiber orientation is favorable tocounteract movement caused by moisture.

To reduce the sound level, floating laminate flooring is installed on asound-absorbing layer of plastic foam, rag paper, textile fiber and thelike. These layers have also been glued to the balancing layer of therear side. This form of sound absorption yields a poor result and thecost is high.

Brief Description of the Invention and Objectives Thereof

The object of the present invention is to eliminate or significantlyreduce one or more of the problems occurring in connection withmanufacture of floating floorboards and in particular such floorboardswith mechanical joint systems. The problems are mainly solved with acore made of at least two layers of different materials or samematerials but with different properties.

Different types of wood such as oak, pine, cork etc and different boardtypes such as MDF, HDF, particle board, plywood, plastic etc areregarded as different materials. These different materials are definedas having different material composition. Same type of material may havedifferent properties if for instance density, strength, flexibility andmoisture resistance properties are different.

The density in a wood fiber based material such as HDF might vary indifferent parts. Such variations in a layer should not be regarded asdifferent properties if the whole layer consist of the same type offibers, binders etc.

The invention is based on the first knowledge that the core should bemade of different layers consisting of different material or of the samematerial but with different properties. This allows the cost of materialto be reduced while at the same time the other properties of thefloorboard, such as impact strength and moisture resistance, can beunchanged.

The invention is based on the second knowledge that a core material withdifferent layers can provide a lower weight without impairing the otherquality properties.

The invention is based on the third knowledge that a core material withdifferent layers can produce better sound properties.

Finally, the invention is based on the fourth knowledge that a corematerial consisting of different layers allows manufacture offloorboards with mechanical locking systems having a high quality whileat the same time the cost can be reduced.

The invention is particularly suited for use in floatingfloors—consisting of floorboards whose-core contains layers of woodfibers, such as wood slats, solid wood, cork, particle board, MDF, HDF,compact laminate, plywood and the like. Such board materials can easilybe glued to each other in different layers and they may, for instance,by impregnating with suitable chemicals, be given improved properties,for instance regarding density, impact strength, flexibility, moistureresistance, friction and the like. In this way, optimal board materialscan be manufactured and combined as regards function and cost level ofthe floorboard and the joint system. Wood-fiber-based materials can beformed to advanced geometries by cutting. The core may also consist ofdifferent plastic materials, rubber materials and the like, which canalso be combined with different wood-fiber-based materials. All the corematerials described above can be formed to floorboards having differenttypes of known mechanical locking systems.

The invention is also particularly suited for use in laminate flooringsand parquet floorings with a lamella core.

Thus, a large number of combinations of different floorboards, lockingsystems, materials and formats can be provided.

The above related objectives are obtained by respective floorboards andsemi manufactures according to the appended independent claims.Embodiments of the invention are set forth in the dependent claims, inthe description and in the drawings.

According to a first aspect of the invention, a floorboard for making alaminate flooring is provided. The floorboard has a core and a surfacelayer comprising a thermosetting resin, arranged on an upper side of thecore. The floorboard is distinguished in that the core comprises atleast two joined layers of material, which are arranged at differentdistances from the surface layer, and which differ in respect ofmaterial properties or material composition, and in that a first corelayer, closest to the surface layer, comprises HDF or MDF.

According to a second aspect of the invention, a semi manufacture formaking the above related laminate floorboard is provided.

Through the first and second aspects of the invention, laminatefloorboards are provided, which enables a reduction of the cost oflaminate floorings by combining the advantages of an HDF or MDF corewith respect to durability and impact strength with the cost advantagesassociated with a less costly floorboard material, such as particleboard. In particular embodiments of the invention, the floorboard mayhave a an upper layer of high-quality HDF and a lower layer of e.g. MDFor particle board.

According to a third aspect of the invention a floorboard for making awood flooring is provided. The floorboard has a core comprising woodlamellae and a surface layer arranged on an upper side of the core. Thecore comprises at least two layers of material, which are arranged atdifferent distances from the surface layer, and which differ in respectof material properties or material composition. The core layer closestto the surface layer comprises HDF or MDF, and the surface layer is awood veneer, which is arranged on said HDF or MDF layer.

According to a fourth aspect of the invention, a semi manufacture formaking the above related wood floorboard is provided.

Through the third and fourth aspects of the invention, the cost offloorboards having a real wood surface and core may be reduced.According to the invention, the amount of wood needed for providing awood surface, which may be reground may be reduced, while maintainingthe floorboard's properties with respect to impact strength.

The invention will now be described in more detail, with reference tothe appended drawings, which show exemplifying embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-d illustrate in different steps manufacture of a floorboard.

FIGS. 2 a-e illustrate the composition of laminate flooring with asurface of high pressure laminate and direct laminate.

FIGS. 3 a-e illustrate examples of different floorboards.

FIGS. 4 a-b illustrate floorboards according to different embodiments ofthe invention.

FIG. 5 illustrates an alternative embodiment of a floorboard accordingto the invention.

FIGS. 6-9 illustrate different embodiments of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 4 a illustrates a preferred embodiment of the invention. Thefloorboard 1 can be, for instance, a laminate or veneer floor. Thethickness can be, for instance, 6-12 mm. In the embodiment illustrated,the floorboard 1 has a surface layer 31 of direct laminate DL, abalancing layer 32 of DL and a core 30 which consists of two layers L1and L2. The upper layer L1 closest to the surface can, for instance, bemade of HDF having high density and moisture resistance. The lower layerL2 can, for instance, be made of a lower quality of HDF, of MDF or ofother wood-fiber-based board materials. A preferred alternative isparticle board. The two layers of material are preferably joined bygluing. In this embodiment there is thus a glue-layer 41 between L1 andL2. Such a floor will have good properties in the upper parts closest tothe surface. Upper joint edges 14 will have high impact strength, andmoisture penetrating between the joint edges will not cause muchproblems. The lower layer L2 of the core may consist of, for instance, aless expensive material, such as particle board of low density. In thismanner, the floorboard will have good properties while at the same timeit can be manufactured at a low cost. The weight will also be lower. Bymaking the core of two materials L1 and L2, the savings in cost that aremade in the lower layer can be used to increase the quality of theupper. The floorboards 1, 1′ can also be made thicker and more stablewith unchanged-weight and cost. The sound level can be reduced by thefloorboard having a different sound frequency which is felt to be morepleasant. The sound level can also be reduced by choosing suitablematerials in the core. An other alternative to reduce the sound is toglue down the floorboard to the sub floor. In this case a mechanicallocking system could be used to position the floor boards and to keepthem together until the glue cures. If a flexible glue is used whichallows some movement of the floor bards relative the sub floor, a semifloating floor could be accomplished with a low sound and tight joints.

FIG. 4 b illustrates a floorboard with a core consisting of 3 layers.The surface layer 31 may be laminate or wood or any other surfacematerial suitable for flooring. L1 and L2 may be made of HDF. L3 may bea softer and more flexible material than the upper layer L1 such naturalor artificial rubber, rubber-like material (e.g. thermoplasticelastomers), plastic foam, textiles, non-wovens or cork. Other soundreducing or absorbing materials may also be used. Such a floor boardwill reduce sound much better than a traditional laminate flooring.A-cork layer combined with an upper layer L1 of HDF and a laminatesurface, especially a direct laminated surface 31 is a preferablematerial. It is easy to glue cork to HDF and cork can stand the heat andpressure resulting from the lamination. The sound reduction could be ofa considerable degree if the sound reducing layer L3 is placed closed tothe surface layer. A preferable embodiment is a floor board with a soundreducing layer L3 in the upper part of the core above the verticallocking means 21 and 22, which in the illustrated embodiment is a groove21 and a tongue 22.

If the layer L3 is made of a flexible and water proof material such asrubber or foam, it could be used to form a joint sealing 23 whichprevents water from penetrating trough the locking system. The layer L3could also be used to include special properties into a laminateflooring. Plastic layers which create heat when connected to electricitymay be used to produce floorboards with floor heating systems integratedinto the core close to the floor surface. The mechanical locking systemcould be formed to automatically connect the heating layers in twofloorboards with each other. Other advanced features may in a similarway be integrated into the core such as layers which activate alarmsystems when a person walks over the floor. All these feature could becombined with a direct lamination production method where the laminationis made against an appropriate wood fiber based material such as HDF.The lower layer L2 could of course be made of other materials than HDF.

According to the invention, floor elements can be made by, for instance,board materials of HDF and particle board being glued to a coreconsisting of two or more layers of material L1 and L2. The HDF board isground in the normal manufacture so as to obtain an even surface anduniform thickness. Such grinding may wholly or partly take placeaccording to the invention after gluing of the layers L1, L2, L3. Inthis way, a saving in material can take place by a smaller amount ofmaterial or less expensive material being removed by grinding. Aftergluing of the core, lamination or gluing of the surface layer takesplace. If the layers of material of the core have the correct thicknesseven before gluing, gluing of the layers of material L1, L2 of the coreas well as the surface layer 3 and the balancing layer 32 can take placein one and the same operation. It is also possible to combine directlaminating with gluing of the layers of material of the core by gluingtaking place using methods that allow complete or partial activation oflayers of glue using the pressure and heat that arise in connection withdirect laminating.

The upper layer of material L1 can be used in the mechanical jointsystem as illustrated in FIGS. 5 and 7. In FIG. 5 a separately machinedstrip 6 of for instance, HDF material has been joined with the core bysnapping-in or angling of the strip tongue 38 into the strip groove 37.This joining can take place in softer materials such as particle board,but the strength may be higher if the mechanical joining takes placewith, for instance, HDF material. The strip tongue 38 has in the upperpart locking means and positioning surfaces which lock the strip 6horizontally and vertically to the floorboard 1. As an alternative, thestrip 6 can also be constructed so as to allow fastening by the striptongue 38 being angled into the strip groove 37 by an angular motioneither from above or from below, but this results in a more complicatedfastening method than snapping-in. The strength of the mechanicallocking system may be lower. In this embodiment according to FIG. 5,also the tongue 22 of the second floorboard 1′ is positioned verticallybetween two HDF materials, which facilitates lateral displacement in thelocked position. This is an important mechanical locking of long andshort sides of rectangular floorboards.

FIG. 6 shows an example of an embodiment of a floorboard according tothe invention which has a relatively thin layer of a hard andmoisture-proof material L1 closest to the surface layer (31).

FIG. 7 shows an example of an embodiment according to the invention of aboard 1 with a core 30 having two materials L1 and L2 of similarthickness. The upper layer of material L1 has been selected so that thelocking system 7, 7′ and its locking means 8, 14 are made of thismaterial.

FIG. 8 shows an example of the condition that the core 30 may consist ofthree layers of material L1, L2 and L2′. The layer of material L1closest to the surface 31 and the lower layer of material L2 closest tothe balancing layer 32 can preferably be identical. This may facilitatebalancing of the board so that it keeps plane as relative humidityvaries. A mechanical locking system with a strip in the lower partaccording to FIG. 4 can be made of this material L2. Moreover, the upperand lower layers of material L1, L2 may be adjusted so as to facilitatelaminating or gluing of surface layer and balancing layer. In thismanner, the material L2′ may be selected in the center layer of thecore, which need not be capable of laminating or easy to glue in anormal gluing process.

FIG. 9 shows an example of a floorboard 1 which constitutes a parquetfloor according to a preferred embodiment of the invention. The surfacelayer 31 consists in this embodiment of a wood layer which is thinnerthan the traditional wood layers. These traditional wood layers are as arule 2-3 mm. According to the invention, the surface layer 31, whichconsists of hard and expensive high-grade wood, can be made with areduced thickness, for instance about 1 mm. This thickness is sufficientto allow regrinding. The varnish systems are today so advanced thatregrinding is in fact not necessary. The remaining part of the woodlayer 31, which is actually only necessary to bridge the irregularitiesof the core of slats, can be provided with a considerably less expensiveand better material L1, for instance HDF. The surface layer 31 ofhigh-grade wood has thus according to the invention been replaced by athin layer of wood and a high quality but less expensive material suchas HDF. We have discovered that in particular HDF with high density is amost convenient material to replace high-grade wood in parquet flooringwith a lamella core. Such a surface layer, which thus consists of a thinlayer of high-grade wood and a core layer of an advanced board material,can be manufactured so that, compared with traditional surface layers ofhigh-grade wood, it will have a better possibility of bridging theirirregularities of the core of slats, be more stable and make lessmovements caused by moisture in case of variations in relative humidity.This can be achieved in combination with a lower cost of material.

Several variants are feasible within the scope of the invention. Thenumber of layers of material in the core can be more than three. Thethickness of the different layers may vary. Special HDF materials can bemanufactured using a significantly larger amount of binder and with anincreased density exceeding 1200 kg/m³. Particle boards with specialbinders and particle sizes can be manufactured so that they areoptimally adjusted to interact with HDF in wood or laminate flooring.Basically, all wood-based board materials can be used that are normallyto be found in the building and furniture industry. The invention is notlimited to thin floors. According to the principles of the invention,laminate flooring can be manufactured in thicknesses exceeding 12 mm,for instance 14-15 mm or more, and with a competitive cost structure andweight. Such thick laminate flooring will as a rule have a more pleasantsound level, which may bridge great irregularities in the subfloor. Theymay be made very rigid and could be used as sports floors. The inventioncan also be used for floorboards without a balancing layer and onfloorboards which are not laid floating but which are glued to thesubfloor.

1. A floorboard for making a wood flooring, the floorboard having a corecomprising wood lamellae and a surface layer arranged on an upper sideof the core, the floorboard having a longitudinal direction and shortdirection orthogonal to the longitudinal direction, wherein the corecomprises at least two layers of material, which are arranged atdifferent distances from the surface layer, and which differ in respectof material properties or material composition, and wherein a first corelayer closest to the surface layer comprises HDF or MDF, and isuniformly dimensioned, and a second core layer comprised of a wood fiberbased material is positioned farther from the surface layer than thefirst core layer, wherein the second core layer comprises slats, theslats are perpendicular to the longitudinal direction of the floorboard,the slats having a fiber orientation which is perpendicular to thelongitudinal direction of the floorboard and perpendicular to the fiberorientation of the surface layer, and the second core layer is directlyattached to the HDF or MDF of the first core layer, wherein said surfacelayer is a continuous sheet of a wood veneer, which is arranged directlyon said HDF or MDF layer.
 2. The floorboard as claimed in claim 1,wherein a thickness of said surface layer is less than 2 mm.
 3. Thefloorboard as claimed in claim 1, further comprising connectors,arranged along at least two opposite edge portions of said floorboard,for connecting said floorboard with a substantially similar floorboardin a vertical direction perpendicular to said surface layer and in ahorizontal direction perpendicular to said vertical direction and tosaid edge portions.
 4. The floorboard as claimed in claim 3, wherein thesaid connectors are designed for connecting the floorboard with saidsubstantially similar floorboard by inward angling and/or snapping-in toa locked position.
 5. A semi manufacture for manufacturing floor-boardsfor wood flooring, said semi manufacture having a core comprising woodlamellae and a surface layer arranged on an upper side of the core, thesemi manufacture having a longitudinal direction and short directionorthogonal to the longitudinal direction, wherein the core comprises atleast two layers of material, which are arranged at different distancesfrom the surface layer, and which differ in respect of materialproperties or material composition, and wherein a first core layerclosest to the surface layer comprises HDF or MDF, and a second corelayer comprised of a wood fiber based material is spaced from thesurface layer by at least the first core layer, wherein the second corelayer comprises slats, and the second core layer is directly attached tothe HDF or MDF of the first core layer, wherein said surface layer is acontinuous sheet of a wood veneer, which is arranged directly on saidHDF or MDF layer, wherein the second core layer slats are perpendicularto the longitudinal direction of the semi manufacture, and the slatshave a fiber orientation which is perpendicular to the longitudinaldirection of the semi manufacture and perpendicular to the fiberorientation of the surface layer.
 6. The floorboard as claimed in claim2, wherein a thickness of said surface layer is between 0.6 and 1.5 mm.7. The floorboard as claimed in claim 1, further comprising connectorsformed in the second layer of the core.
 8. The floorboard as claimed inclaim 7, wherein the connectors comprise a locking groove arranged alonga first edge portion of the two opposite edge portions and a connectingtongue arranged along a second edge portion of the two opposite edgeportions.
 9. The floorboard as claimed in claim 1, further comprising abalancing layer, wherein the core is positioned between the balancinglayer and the surface layer.
 10. The semi manufacture as claimed inclaim 5, further comprising a balancing layer, wherein the core ispositioned between the balancing layer and the surface layer.
 11. Thefloorboard as claimed in claim 9, wherein the balancing layercompensates for a variation in relative humidity so as to maintain aplane of the floorboard.
 12. The floorboard as claimed in claim 9,wherein the balancing layer is a direct laminate.
 13. The floorboard asclaimed in claim 9, wherein the balancing layer is a veneer.
 14. Thesemi manufacture as claimed in claim 10, wherein the balancing layer isa direct laminate.
 15. The semi manufacture as claimed in claim 10,wherein the balancing layer is a veneer.